The ratio itself does not mean that the rise in pedestrian fatalities is significant. Consider 0.00000000000000001% population growth and a 0.000001% rise in fatalities, or any number of zeroes that you like.
The per capita or per 100,000 rise would be meaningful. You don't get the per capita rise by dividing the rise in fatalities by the rise in population growth.
No, it doesn't mean that the rise in pedestrian fatalities is significant, it means that there is something that is causing a rise in pedestrian fatalities (and that it isn't simply population growth).
I agree the numbers used in the article are not the most explicit, though.
The per capita or per 100,000 rise would be meaningful. You don't get the per capita rise by dividing the rise in fatalities by the rise in population growth.